The present invention is directed to new and useful improvements in filter cartridges and in particular to methods for making precision wound tubular shaped filter cartridges comprises of helically wound multiple layers of yarn or roving.
It is well known to provide filter cartridges for purifying liquid input streams wherein the cartridge comprises a tubular element having a foraminous core about which layers of spaced convolutions of fibrous filter yarn are precision wound. The yarn is applied in crisscross fashion to form a plurality of diamond shaped filtering passageways from the outer surface of the element to the foraminous cores. As fluid passes through the filter element through the diamond shaped passageways dirt particles or the like in the fluid are captured among the fibrous yarn strands which may be napped to provide additional dirt capturing fibers.
In general, precision wound filters are formed by mounting the foraminous core in a horizontal position on a motor driven spindle. One end of the strand of filtering material is tied or otherwise fixed to one end of the sidewall of the core. The strand passes through a guide which is aranged through a gear train or similar arrangement to maintain a precise relationship between rotations of the core and traverse of the guide, to move back and forth along the length of the core, as the core is rotated. As the guide travels in one direction along the rotating core, a spiral or strand is wrapped around the core from one end to the other. When the guide reaches the far end of the core, it reverses in direction and travels back to the beginning point. During this travel in a reverse direction, the core continues to rotate in the same direction. In this manner a reverse spiral of strand is laid down on the core overlaying the original strand spiral, forming a diamond pattern which provide passageways for the fluid to be filtered.
Typical filter cartridges have a foraminous core with a diameter of about 11/8 inches and an overall diameter of about 2 7/16 inches with a filter medium (i.e. the buildup of fibrous strands on the core) being about 11/16 inches thick. The standard length of the filter cartridge is 10 inches for insertion in a suitable file housing. The ratio of circumferential diamond shaped passages to axial diamond shaped passages is usually within the range of about 2 to about 5 whereby for each circumferential diamond there are about 2 to 5 axial diamonds.
Since these filter cartridges are disposable and replaceable once they reach their rated dirt holding capacity there have been many prior art efforts to increase the useful life and dirt holding capacity of these cartridges within the previously mentioned required dimensional restrictions.
In one known type precision wound filter cartridge of the type described it is known to provide a filter medium comprised of layers of different densities (wind geometries) wherein the inner layer or base wind is provided with a greater number of circumferential diamonds than the outer layer or wind to improve the efficiency of the cartridge over mono-layer wound cartridges.
Although these known multi-layer filter cartridges are meant to maintain efficiency and maximize filter characteristics of the cartridge problems are encountered in preventing the plugging of the radial helically disposed flow passageways due to restrictions in the flow patterns of the diamond shaped passageways occurring at the interface between adjacent layers. The communication of passageways and the interlayer restrictions between layers resulted in the loss of efficiency and shortening of the useful life span of the filter cartridge. It was found that in the positioning of layers the roving strands in the more open outer layer restricted access of fluid to the channels in the tighter inner layer adjacent the core. These flow restrictions were found to cause a higher pressure drop and thus a decrease in dirt holding capacity and a plugging of the radial passageway.
It is an object of the present invention to provide a novel multiple layer precision wound filter.
Another object is to provide a novel multilayer filter cartridge having increased dirt holding capacity.
A still further object is to provide a multiple layer filter cartridge wherein flow restrictions between adjacent layers is greatly reduced through novel positioning of the radial flow passages between adjacent layers.